1. Field of the Invention
The present invention relates to a solid-state imaging device, a method for manufacturing the solid-state imaging device, and an electronic apparatus including the solid-state imaging device.
2. Description of the Related Art
Solid-state imaging devices are roughly classified into charge transfer type solid-state imaging devices typified by a CCD image sensor and amplification type solid-state imaging devices typified by a CMOS image sensor. In this regard, “CCD” is the abbreviated name for a charge coupled device, and “CMOS” is the abbreviated name for a complementary metal oxide semiconductor.
A CCD solid-state imaging device includes an imaging region including a plurality of light-receiving portions arranged two-dimensionally, that is, photodiodes serving as photoelectric conversion elements, and vertical transfer resister portions which are arranged in accordance with the individual photodiode lines and which have a CCD structure. The CCD solid-state imaging device is configured to further include a horizontal transfer resister portion having a CCD structure in which a signal charge from the imaging region is transferred in the horizontal direction, an output portion, a peripheral circuit constituting a signal processing circuit, and the like.
A CMOS solid-state imaging device is configured to include a pixel portion (imaging region), in which a plurality of pixels including photodiodes serving as photoelectric conversion elements constituting light receiving portions and a plurality of pixel transistors are arranged two-dimensionally, and a peripheral circuit portion, e.g., signal processing, disposed around the pixel portions. The pixel transistor is formed from a MOS transistor.
Regarding these solid-state imaging devices, in order to increase the light-condensation efficiency of incident light along with the pixel being made finer, the configurations, in which waveguides including clad layers and core layers having different refractive indices are provided in accordance with the individual photodiodes, have been proposed. Solid-state imaging devices provided with a waveguide function are disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2000-150845, Japanese Unexamined Patent Application Publication No. 2003-324189, Japanese Unexamined Patent Application Publication No. 2004-221532, Japanese Unexamined Patent Application Publication No. 2005-294749, and Japanese Unexamined Patent Application Publication No. 2006-86320.
FIG. 29 and FIG. 30 show an example of a CCD solid-state imaging device in the related art. FIG. 29 is a plan view of a key portion of an imaging region. FIG. 30 is a sectional view of the section taken along a line XXX-XXX shown in FIG. 29. As shown in FIG. 29, in a CCD solid-state imaging device 100, usually, photodiodes (PDs) serving as square light-receiving portions 101 are arranged two-dimensionally and vertical transfer resister portions 102 having a CCD structure to transfer signal charges in the vertical direction are disposed in accordance with the individual light-receiving portion lines. The vertical transfer resister portion 102 is configured to include a buried transfer channel region 103 and a plurality of transfer electrodes 104, 105, and 106 disposed thereon with an gate insulating film therebetween. In the present example, a plurality of transfer electrodes 104, 105, and 106, which are formed from a polysilicon film serving as a first layer, are disposed in such a way that a photodiode (PD) serving as one light-receiving portion 101 is associated with three transfer electrodes.
The transfer electrodes 104 and 106 are disposed continuously in the horizontal direction while being passed between light-receiving portions 101, which are adjacent to each other in the vertical direction, in such a way that electrodes of individual vertical transfer resister portions 102 are connected to each other, where the electrodes correspond to each other. On the other hand, the individual transfer electrodes 105 doubling as reading electrodes are disposed independently in the shape of an island and, therefore, are connected to a connection wiring 107 formed from a polysilicon film serving as a second layer. This connection wiring 107 is configured to include a band-shaped portion 107B disposed on the transfer electrodes 104 and 106 extending between the light-receiving portions 101, which are adjacent to each other in the vertical direction, with an insulating film therebetween and an extension portion 107A which is integrated with the band-shaped portion 107B and which is extended on each of the individual transfer electrodes 105. This extension portion 107A is connected to a contact portion 108 of each of the transfer electrodes 105 in the individual vertical transfer resister portions 102.
In the cross-sectional structure shown in FIG. 30, a second electrical conduction type, for example, a p-type first semiconductor well region 112 is disposed on an n-type, which is a first electrical conduction type, semiconductor substrate 111. A photodiode (PD) serving as a light-receiving portion 101 is disposed in this p-type first semiconductor well region 112. The photodiode (PD) is disposed including an n-type semiconductor region 113 and a p-type semiconductor region 114 to suppress a dark current. In the p-type first semiconductor well region 112, an n-type buried transfer channel region 115 and a p+ channel stop region 116 are further formed and a p-type second semiconductor well region 117 is disposed immediately under the buried transfer channel region 115.
The transfer electrodes 104 to 106 formed from the first layer polysilicon are disposed on the buried transfer channel region 115 with a gate insulating film 118 therebetween, and the connection wiring 107 which is formed from the second layer polysilicon and which is connected to the island-shaped transfer electrode 105 is disposed with an insulating film 119 therebetween. The gate insulating film 118 is formed from, for example, a silicon oxide film, and the insulating film 119 is formed from, for example, a silicon nitride film. A light-shielding film 120 is disposed in such a way as to cover the transfer electrodes 104 to 106 and the connection wiring 107 except the photodiode (PD) with the insulating film 119 therebetween. The light-shielding film 120 is not disposed on the photodiode (PD). On the surface of the photodiode (PD), an insulating film 121 formed from, for example, a silicon oxide film and, for example, a silicon nitride film serving as an antireflection film 122 extended from the silicon nitride film, which serves as the insulating film 119 on the above-described transfer electrodes 104 to 106 side, are disposed.
Waveguides 124 to condense incident light effectively on the photodiode (PD) are disposed above the individual photodiodes (PD). The waveguide 124 includes a core layer 125 formed from, for example, a silicon nitride film having a high refractive index and a clad layer 126 formed from, for example, a silicon oxide film surrounding the core layer 125 and having a low refractive index. The waveguide 124 shown in FIG. 30 is configured in such a way that the bottom of the core layer 125 comes into contact with the silicon nitride film serving as the antireflection film 122.
Furthermore, a passivation film 130 is disposed, an on-chip color filter 128 is disposed thereon with a planarizing film 127 therebetween, and an on-chip microlens 129 is disposed thereon.
The respective widths of the extension portion 107A and the band-shaped portion 107B of the connection wiring 107 may be smaller than the width of the transfer electrode 105 and the widths of the transfer electrodes 104 and 106 between pixels adjacent to each other in the vertical direction. Alternatively, although not shown in the drawing, the respective widths of the extension portion 107A and the band-shaped portion 107B of the connection wiring 107 may be the same as the width of the transfer electrode 105 and the widths of the transfer electrodes 104 and 106 between pixels adjacent to each other in the vertical direction.
The waveguide 124 is formed as described below. After the light-shielding film 120 is formed, a silicon oxide film serving as the clad layer is formed all over the surface in such a way as to fill the inside of an opening portion surrounded by the light-shielding film 120 above the photodiode (PD). Subsequently, selective etching of the silicon oxide film is conducted by using a resist mask so as to form a trench portion at a location in accordance with the photodiode (PD). At the same time, the silicon oxide film remaining as the side wall of the trench portion constitutes the clad layer 126. Thereafter, the core layer 125 formed from, for example, a silicon nitride film is embedded into the trench portion surrounded by the clad layer 126, so that the waveguide 124 including the clad layer 126 and the core layer 125 is formed.